Field of the Invention
The present invention relates to an image pickup apparatus such as a monitoring camera with shock resistance.
Description of the Related Art
In some conventional monitoring cameras with shock resistance property, a dome cover for covering a lens unit is made of a material such as shock-resistant polycarbonate resin, and an exterior housing for covering a main body of the camera is made of metal to achieve the shock resistance property. However, as compared with the exterior housing made of metal, the dome cover made of resin may be momentarily deformed to a great extent by a shock, even if the dome cover is not damaged. For this reason, if a shock over a certain energy level is applied to the monitoring camera, the dome cover is deformed by the shock, and the deformed dome cover may contact an inner structure such as the lens unit, resulting in a damage of the inner structure.
As an example of a conventional technique to solve such an issue, a monitoring camera is discussed in which a rotation base serving as a supporting member supporting a camera unit is fixed with shaft screws, which are each inserted into a vertically extending elongate hole provided in a support of a rotary bracket. In this example, the rotation base can be supported to be rotatable in the vertical direction and linearly movable in the vertical direction with a simple structure, thereby absorbing a shock when a cover is hit, so that damage to the camera unit can be prevented (see Japanese Patent Application Laid-Open No. 2003-174572).
The conventional monitoring camera with shock resistance property has a structure in which the lens unit is retracted when the dorm cover is deformed by a shock applied to the dome cover, and thus preventing a damage. A deformation amount of the dome cover in receiving a shock depends on the wall thickness and the diameter of a hemispherical shape of the dome cover. The smaller the wall thickness, the greater the deformation amount. The larger the diameter of the hemispherical shape, the greater the deformation amount of the dome cover.
Further, as the wall thickness is greater, or as the diameter of the hemispherical shape is smaller, an influence exerted by the dome cover on optical performance of the lens unit is greater because the dome cover acts as an optical component. When a lens unit with high-magnification and high-telephoto zoom capabilities is employed, the influence on the optical performance is even greater, which may cause degradation in resolution. Therefore, a monitoring camera equipped with the high-magnification and high-telephoto lens unit is desirably configured in such a manner that the wall of the dome cover is as thin as possible, and that the diameter of the hemispherical shape is large.
However, in the conventional monitoring camera with shock resistance property, if the dome cover has a thinner wall and a larger diameter, the deformation amount of the dome cover due to a shock increases. This increases the amount of retraction necessary for the lens unit, which leads to an increase of the size of the monitoring camera.